Finding the Third Proportional to 31,128 and 39,990

Step by Step Solution

1. Step 1: Write the proportion equation
   31,128 : 39,990 = 39,990 : x
2. Step 2: Convert to fraction form
   31,128/39,990 = 39,990/x
3. Step 3: Cross multiply
   31,128x = 39,990 × 39,990
4. Step 4: Simplify right side
   31,128x = 1,599,200,100
5. Step 5: Solve for x
   x = 1,599,200,100/31,128
6. Step 6: Final answer
   x = 51,374.97